The cyano-substituted cyclopropane derivatives of the present invention are useful intermediates in the manufacture of 2-(2,2-dihalovinyl)-3,3-dialkylcyclopropanecarboxylic acids and their corresponding alkyl esters which are themselves key intermediates in the manufacture of a group of compounds known as "synthetic pyrethoids" which exhibit remarkable levels of insecticidal and acaricidal activity. U.K. Pat. No. 1,413,491 discloses and claims in important group of these synthetic pyrethoids, for example, the 3-phenoxybenzyl ester of 2-(2,2-dichlorovinyl)-3,3-dimethylcyclopropanecarboxylic acid is an insecticidally active compound. An examination of U.K. Pat. No. 1,413,491 demonstrates the difficulty in synthesizing the carboxylic acid precursors employed in the preparation of the insecticidally active compounds. One method employed comprises the ozonolysis of an ester of chrysanthemic acid, the product of ozonolysis is then used in a Wittig reaction to generate the desired dihalovinyl substituted cyclopropane carboxylate. This difficulty in synthesizing the appropriate cyclopropane carboxylic acid precursors has prompted other researchers to expend considerable effort in attempting to find a simpler route to the synthesis of the above-mentioned cyclopropanecarboxylic acid--see for example Netherlands patent application 7,510,479 and 7,509,631--and, so far, all published routes to this acid are cumbersome and involve many process steps.
The Applicant has discovered the following key intermediates for the simple manufacture of the above-mentioned desired acids: ##STR2## wherein for the production of 2-(2,2-dichlorovinyl)-3,3-dimethylcyclopropanecarboxylic acid Hal represent chlorine and R.sub.1 and R.sub.2 represent methyl, and for the production of other cyclopropanecarboxylic acid precursors useful in the process described in U.K. Pat. No. 1,413,491 Hal represents a fluorine, chlorine or bromine atom and R.sub.1 and R.sub.2 each, independently, represent an alkyl group of one to four carbon atoms. It will be appreciated that the above-defined intermediates can be readily converted by known methods, such as, for example, hydrolysis of the cyano group, into the corresponding cyclopropanecarboxylic acid and/or their corresponding alkyl esters.